Cold, salinity, and drought restrict the range available for crop production. Corn production serves as an example. Within the United States, corn is cultivated in 26 states. The northern most boundary of corn production is within North Dakota and Minnesota and the western extreme is in Colorado. Even within this area states such as South Dakota are affected by drought, leading to low yields. Outside of this area, drought prohibits substantial cereal cultivation in states such as Arizona.
Similarly, in Canada there are risks associated with extending corn acreage. Last year alone corn production declined nearly 7.0% in the prairie provinces largely due to above average temperatures and dry conditions. The inability to effectively manage these environmental challenges is partially responsible for 96% of Canadian corn production remaining in Quebec and Ontario. This fact coupled with depression of feed prices in the prairie provinces, make expanded corn cultivation particularly risky in areas in Canada where unpredictable environmental challenges abide.
Crop production must meet the needs of the population, but population increases are expected worldwide. Population increases will be most significant in the developing nations where growth of 3.6%, 3.0%, 2.1% and 2.0% are expected in the southern Mediterranean, in the sub-Sahara, in the central Asian republics, and on the Indian subcontinent respectively. With population increases, the demand for crops will increase in developing nations. In contrast, drought reduces the annual corn harvest by 20 million tons and is second only to soil infertility as a constraint on corn production in the developing world.
Environmental stresses not only restrict corn production, but all crops are restricted. In addition crops are required not only for food, but for other products such as fuel, animal feed, paper, food additives, et cetera. A need exists to extend the range of crop production.
C-repeat Factors (CBFs) or Dehydration Responsive Element factors (DREB1s) are transcription factors, which induce several genes which in turn confer tolerance to freezing temperatures, drought, or salinity stresses in plants (Jaglo-Ottosen et al. (1998) Science, 280(5360): 104-6; Kasuga et al. (1999) Nat. Biotechnol. 17(3): 287-91). Various reported DREB1s are expressed differently depending on the nature of the stress to which the plant is exposed. Table 1 lists CBF genes and their induction pattern in response to environmental stress. DREB1D and DREB1F were reported to be induced only by salinity stress in the roots of Arabidopsis (Sakuma et al. (2002) Biochem. Biophy. Res. Commun. 290(3): 998-1009). While rice OsDREB1A is induced by cold and salinity stresses (Dubouzet et al. (2003) Plant J. 33(4): 751-63), and Arabidopsis CBF4 is only induced by drought stress (Haake et al. (2002) Plant Physiol. 130(2): 639-48).
CBF genes induced by cold treatment at 4° C. have been reported (Gimour et al. (1998) Plant J. 6(4): 433-42, Liu et al. (1998) Plant Cell. 10(8): 1391-406, Medina et al. (1999) Plant Physiol. 119(2): 463-70, Gao et al. (2002) Plant Mol. Biol. 49(5): 459-71). In Arabidopsis cold induced CBF genes are uniformly and highly induced upon cold stress. However, in previously reported CBF cold tolerance cases, transgenic plants constitutively overexpressing CBF genes are stunted and the severity of stunting positively correlates with the level of CBF gene expression in the transgenic plants (Liu et al. (1998) Plant Cell. 10(8): 1391-406). Other CBF genes and their expression profiles are discussed in Chen et al. (2003) Theor. Appl. Genet. 107(6): 971-9; Choi et al. (2002) Plant Physiol. 129(4): 1781-7; Jaglo et al. (2001) Plant Physiol. 127(3): 910-7; Qin et al. (2004) Plant Cell Physiol. 45(8): 1042-52; and Zhang et al. (2004) Plant J. 39(6): 905-19. Each of the above references is incorporated by reference as if fully set forth herein.
TABLE 1CBF/DREB1 Genes and their Induction PatternInduced byCBF GeneColdDroughtSalinityArabidopsis CBF1•∘—Arabidopsis CBF2•∘—Arabidopsis CBP3•∘—Arabidopsis DREB1A•∘∘Arabidopsis DREB1B•∘∘Arabidopsis DREB1C•∘∘Arabidopsis CBF1•∘—Arabidopsis CBF2•∘—Arabidopsis CBF3•∘—Brassica BnCBF•——Rye ScCBF•——Wheat CBF TaCBF•——Tomato CBF LeCBF•——Barley HvCBF3•——Brassica BNCBF5•∘—Brassica BNCBF7•∘—Brassica BNCBF16•∘—Brassica BNCBF17•∘—Arabidopsis DREB1D∘∘•Arabidopsis DREB1E∘∘∘Arabidopsis DREB1F∘∘•Arabidopsis CBF4∘•∘Rice OsDREB1A•∘•Rice OsDREB1B•∘∘Rice OsDREB1D∘∘—Rice OsDREBL•∘∘Tomato LeCBF1•∘∘Tomato LeCBF2∘∘∘Tomato LeCBF3∘∘∘Petunia ZmBREB1A•——[Legend: • Induced; ∘ Not Induced; — Not known]
There is a need for control of stress tolerance in plants that includes differential response to various stresses, including cold temperatures. There is also a need for producing stress tolerance in plant which does not result in deleterious traits such as stunting. In addition, there is a need for control of stress response in plants which extends not only to one or two environmental stresses, but to at least three.